The present invention relates to an end effector, and more particularly, to an end effector suitably used for clamping an object which is located in such a manner that the position or angle thereof is relatively unstable, for example in outer space.
A, as a standard end effector (SEE) for use in a remote manipulator system (RMS) for space crafts is disclosed in U.S. Pat. No. 4,105,241.
The conventional end effector of the type described above is controlled by a sequence of steps such that a dedicated object to be clamped, called a "Grapple fixture", first captured, is pulled in, and then is rigidized. Once the capturing operation is started, a payload mass up to of 30t needs to be captured in a short time against an inertial force thereof. If a misalignment between the position and angle of the end effector and those of the grapple fixture is too large, the above-described inertia force produces an extremely large force (or a torque). Therefore, a problem arises that such excessive force accelerates the degradation of a lubricative function in a vacuum state of the elements for transmitting the clamping force, such as a driving system, rotary rings, ball screws and so forth, and thereby the life of the same is shortened because the use of lubricants is extremely restricted in the space.
On the other hand, since an RMS has a great overall size exceeding 10m and involves a narrow visual range, it is difficult to align the orientation of the RMS with the center of gravity of the payload. Therefore, an excessive force needs to be applied to the SEE for the purpose of capturing grapple fixtures.